Prove Me Wrong! Why BMI Could Actually Discourage Training!
By Charles Staley, B.Sc, MSS
Director, Staley Training Systems
Author’s note: I wrote this when the BMI index began making the news. It struck me that the BMI actually discourages training— see if you agree.
Warning! Exercise Increases Your Risk of Weight-Related Health Problems
The BMI is designed to replace the old height/weight charts created by health insurance companies. But the question remains, what is the accuracy, not to mention, the utility, of the BMI?
First, let's start with a definition. You can calculate your BMI by dividing your weight in kilograms by your height in meters squared. (If you'd prefer to spare yourself the mathematical trauma, just head over to The Department of Health and Human Services at http://www.nhlbisupport.com/bmi/ (they have a BMI calculator which you can use to instantly calculate your supposed level of risk of overweight.)
An Interesting Test Case: Me
I recently did just that, and at 205 pounds and a height of 6'1", I landed a whopping BMI of 28— nearly obese by BMI standards.
According to the NIH, you'll need a BMI of 24 or less in order to qualify as having a "normal" weight. So I kept plugging in lower and lower bodyweights, finally going all the way down to 180 pounds to obtain a BMI of 24.
I wonder, what would the consequences of losing 25 pounds be for me? Of course, a fairly large portion of this weight would be muscle— If I make the assumption that I'm currently 15% bodyfat, that means I only have 30.75 pound of fat on my entire body. So, to lose 25 pounds without losing any muscle, I'd end up with less than 2% bodyfat, which is probably not enough to sustain life.
So, that means that the 25 pounds would be mostly muscle. Since a pound of muscle burns approximately 18 calories a day, my metabolic rate would be lowered by 450 calories a day.
Also, this dramatic loss of muscle would certainly profoundly reduce my strength levels. While I have more than enough strength to get through my daily activities, muscle mass and strength both gradually decline as we age.
So I always look at muscle like "money in the bank:" the more I have now,
the more I'll still have when I'm 60, 70, or 80 years of age. So the bottom line seems to be, if I choose to adhere to NIH's guidelines, my health and functional status will surely decline!
Another very important point to consider are the legions of people who will score very acceptable numbers using the BMI, but who in fact are overfat. Despite what many people think, it’s common to find people who appear to be of normal or even low bodyweight, who in fact are overfat, because they have such low levels of muscle mass.
Consider the research conducted by Dr. William Evans at Tufts University: Evans discovered that the as women age, in many cases their leg girth tended to remain constant, however, upon CAT scan analysis, it was found that the fat mass was increased, while the lean mass had decreased. In other words, their external appearance had not significantly changed, yet their bodyfat percentage had increased.
And Even Further...
Because muscle weighs more than fat, embarking on a rapid, unhealthy weight-loss scheme will reduce your BMI much more effectively than losing weight in a healthy and rational manner (the faster you lose weight, the more muscle you lose). So I would like to venture the proposition that the new BMI will encourage fad weight loss programs and starvation diets.
Is There a Better Alternative?
Yes. Have a reputable fitness professional measure your bodyfat percentage (call the International Sports Sciences Association at (800) 892-ISSA to find such a professional in your area). Over the past several years, there have been important new developments in bodyfat measurement techniques, and today, there are several options available. Various methods have varying degrees of accuracy, but if you always use the same method, you’ll have an accurate standard of reference.
In other words, you may not know your exact percentage of bodyfat, but you’ll know if your percentage is increasing or decreasing.
I don’t know why this is such a hard pill to swallow— it’s bodyfat, NOT bodyweight that determines your health and functional capacity. There will never be a height/weight chart, regardless of what anyone chooses to call it, which can predict optimal bodyweight, because such charts never take a person’s muscle mass into account.